I was at a customer site last week to help them with planning for a WebSphere AppServer Migration. They had started doing some work earlier, had some "challenges" and made some subsequent calls. After our meeting they gave me the quote in the title. In this, like in many cases, an ounce of prevention is worth a pound of cure. For example, when moving to WebSphere AppServer v6.1 you can no longer directly access our jars in the /lib directory reliably. Some of them have moved and they have to be properly initialized. The appropriate way to reference our jars is to call our setupCmdLine from your script to setup the classpath.
The problem is you have to find the prevention (in this case information) before the pain occurs. We believe we have some help, check out this site for planning, tips and "gotcha's" before migrating WebSphere AppServer versions: